1. Field of the Invention
This invention relates generally to a fiber-reinforced composite material, and more particularly to a fiber cement building material utilizing a blend of bleached and unbleached cellulose fibers as reinforcing fibers, including formulations, methods of manufacture, and final products.
2. Description of the Related Art
Fiber-reinforced composite materials have been used to form various building products such as building sheets, panels, planks and roofing material. The reinforcement fibers used in these building products typically include natural and synthetic fibers such as metal fibers, glass fibers, asbestos fibers, and cellulose fibers such as those described in Australian Patent No. 515151 and U.S. Pat. No. 6,030,447, which are hereby incorporated by reference in their entirety. Presently, cellulose fiber is one of the preferred fibers for most commercial building material applications because it is an effective, low cost, and recyclable natural product that is compatible with most conventional fiber cement manufacturing processes such as refining and autoclaving.
The performance characteristics of most cellulose fiber reinforced building materials are highly dependent on the quality and characteristic of the cellulose fibers used. In particular, the species and grade of cellulose fibers can have a significant impact on the flexibility and strength of the building material. For example, unbleached, premium grade cellulose fibers derived from Pinus Radiata are known to provide the resulting product with higher strength because these fibers typically have longer length and favorable strength-related properties. Conversely, unbleached, standard grade cellulose fibers derived from a variety of other commonly available wood species such as Douglas fir, hemlock, spruce, white fir, southern pine, and redwood are generally shorter and/or weaker, imparting lower strength and flexibility to the product.
However, there are several disadvantages associated with the use of premium grade cellulose fibers. First, the source of premium grade cellulose pulp has been largely limited to one particular species of wood. The cost of such fibers is also significantly higher than other grades of unbleached pulp. Moreover, limited availability of premium grade pulp can place severe constraints on fiber cement manufacturing operations and ultimately drive up the cost of the product. As such, product manufacturers typically incorporate both premium grade and standard grade unbleached pulps in fiber-cement composite materials in order to provide a final product with adequate strength and flexibility at minimum cost.
Even so, unbleached standard grade Kraft pulps typically used for fiber cement are considered specialty grades of cellulose pulp and are sold at a premium price over other types of cellulose pulp commonly used in paper, linerboard or other cellulose pulp based products.
Hence from the foregoing, it will be appreciated that there is a need for a readily available, less costly substitute for premium grade cellulose fibers for use in the manufacturing of fiber cement composite materials. To this end, there is a particular need for a cellulose fiber that will provide fiber cement composite materials with substantially equal if not improved strength, flexibility and other physical properties as compared to equivalent composite materials reinforced with premium grade cellulose fibers.